Datasheet

Application notes LED2000
12/40 DocID023432 Rev 4
6 Application notes
6.1 Closing the loop
Figure 5. Block diagram of the loop
6.2 G
CO
(s) control to output transfer function
The accurate control to output transfer function for a buck peak current mode converter can
be written as:
Equation 1
where R
0
represents the load resistance, R
i
the equivalent sensing resistor of the current
sense circuitry, 
p
the single pole introduced by the LC filter and 
z
the zero given by the
ESR of the output capacitor.
F
H
(s) accounts for the sampling effect performed by the PWM comparator on the output of
the error amplifier that introduces a double pole at one half of the switching frequency.
V
IN
-
+
-
LC filter
V
REF
error
amplifier
FB
compensation
network
PWM
comparator
HS
switch
R
S
L
C
OUT
R
C
C
C
+
PWM control
Current sense
LS
switch
V
OUT
V
CONTROL
G
CO
(s)
A
O
(s)
α
LED
G
CO
s
R
0
R
i
------ -
1
1
R
0
T
SW

L
----------------------- m
C
1D–0,5–+
----------------------------------------------------------------------------------------
1
s

z
------+


1
s

p
------+


---------------------- F
H
s=